The present invention relates to nonwoven fabric rolls, made by winding up onto a tube a nonwoven fabric formed from thermoplastic elastomer filaments, and methods and apparatus for producing nonwoven fabric rolls.
Nonwoven fabrics are commonly produced by spinning a thermoplastic resin into fibers, and allowing the freshly spun fibers to pile on a moving conveyor belt. Entangled filaments bond with each other due to the high self-adhesive properties of the still-hot thermoplastic elastomer, thereby forming a sheet of nonwoven fabric. The sheet is typically compressed in some manner to produce the desired thickness and density. The nonwoven fabric, formed into a sheet, is then transported by the belt conveyor toward nip rollers which peel the fabric from the belt conveyor. Then the nonwoven fabric is wound up by a take-up device around a cylindrical core to form a nonwoven fabric roll.
Since the freshly spun thermoplastic elastomer has highly adhesive properties, the spun filaments tend to adhere to the belt conveyor as well as to one another. As a result, it is necessary to apply a significant amount of tension to the nonwoven fabric to peel it from the belt conveyor.
Consequently, when the nip rollers peel the nonwoven fabric from the belt conveyor, a tension due to the adhesion acts on the nonwoven fabric causing the fabric to stretch, while shrinking in the direction of width, with the formation of longitudinal wrinkles. In prior art apparatus and methods, because the nip rollers are disposed downstream of the nonwoven fabric, the tension Ta acting on the nonwoven fabric being peeled off is significantly greater than the force F required for peeling off, as shown in FIG. 11. Thus the nonwoven fabric production apparatus of the prior art has problems in that a very large tension is exerted on the nonwoven fabric when peeling it off the belt conveyor, resulting in wrinkles formed along the length of the nonwoven fabric. The longitudinal wrinkles are then fixed on the nonwoven fabric as the wrinkled fabric is pressed between the nip rollers.
Also, because the tension caused by the nip rollers acts between the nip rollers and the take-up device as well, the nonwoven fabric is tightly wound up around the tube while under tension. The nonwoven fabric roll wound by the take-up device is used in the production of many products, such as first aid bandages or gloves, by punching the nonwoven fabric after unrolling it from the roll. Since the nonwoven fabric roll is wound tightly, a nonwoven fabric roll that has been left for a long period of time becomes difficult to unroll, partly due to the self-adhesive properties of the thermoplastic elastomer. As a result, there has also been a problem in that significant tension must be applied to unroll the nonwoven fabric, which causes an elastic deformation wherein the nonwoven fabric stretches lengthwise and shrinks in the direction of width. This deformation is spontaneously reversed after a period of time (delayed restoration), after the punch forming process, thus causing a change in the punched shape.
There is a need for nonwoven fabric rolls which do not exhibit longitudinal wrinkles, and which may be unwound with little or no deformation so that delayed restoration does not lead to a change in shape of derived products. There is also a need for methods and apparatus for producing nonwoven fabric rolls having such properties.
It is an object of the present invention to provide a thermoplastic elastomer nonwoven fabric roll exhibiting reduced wrinkles and reduced change in shape associated with delayed restoration. It is a further object of the invention to provide a method and apparatus for producing such a roll.
The invention relates to a nonwoven fabric roll formed by winding a nonwoven fabric, formed from thermoplastic elastomer filaments accumulated and bonded into a sheet, around a tube, wherein the nonwoven fabric roll is formed so that the tension (unrolling tension) exerted on the nonwoven fabric when being unrolled from the nonwoven fabric roll is not greater than 0.25 g/cm/basis-weight.
When the unrolling tension exceeds 0.25 g/cl/basis-weight, it becomes necessary to apply an excessive tension to the nonwoven fabric when unrolling the nonwoven fabric roll. This causes the nonwoven fabric to experience such an elastic deformation as stretching in the direction of length and shrinking in the direction of width and, when the nonwoven fabric is punched to form a product, the punched shape changes due to delayed restoration of the elastic deformation, thus making it impossible to produce good products. When strictly taking the change in shape due to delayed restoration into consideration, the unrolling tension is preferably 0.20 g/cm/basis-weight or less, and more preferably 0.15 g/cm/basis-weight or less.
According to this invention, the filaments that are spun from the spinning device are piled up and bonded to form a sheet of nonwoven fabric on the belt conveyor. The nonwoven fabric thus formed is carried by the belt conveyor and peeled from the belt conveyor by a rotating roller disposed above the transportation zone, to be wound by the take-up device around the tube to make the nonwoven fabric roll.
As mentioned previously, since the thermoplastic elastomer has highly adhesive property, the filaments that are spun therefrom tend to adhere to the belt conveyor. As a result, it is necessary to apply a significant amount of tension to the nonwoven fabric to peel off the nonwoven fabric from the belt conveyor. According to this invention, since the nonwoven fabric is peeled from the belt conveyor by the lifting action of the rotating roller disposed above the transportation zone of the belt conveyor, substantially the same tension as exerted on the nonwoven fabric is applied to peel off the nonwoven fabric. As a consequence, the nonwoven fabric can be peeled from the belt conveyor by applying only the minimum tension that is necessary and sufficient, thus making it possible to minimize the elastic deformation and longitudinal wrinkling of the nonwoven fabric that are caused when peeling off.
Since the tension is reduced as described above, the tension acting on the nonwoven fabric between the rotating roller and the take-up device is also reduced, so that the nonwoven fabric is wound up into a roll with a lower tension. As a result, the nonwoven fabric roll thus formed is wound less tightly. Thus even under the influence of the adhesive property that is characteristic to the thermoplastic elastomer, the nonwoven fabric roll that can be easily unrolled with an unrolling tension of 0.25 g/cm/basis-weight or less can be formed. Such a nonwoven fabric roll having favorable unrolling performance requires a relatively lower tension to unroll the nonwoven fabric, and makes it possible to minimize the change in the punched shape due to delayed restoration.